Among the steroid hormones progesterone is unique inasmuch as its presence is important in female mammals, particularly in women, for the maintenance of a successful pregnancy. A loss or interference with progesterone during the early stages of mammalian pregnancy prevents the continuation of gestation. Indeed, the loss of progesterone in the very early stages of a human pregnancy prevents either the implantation of the blastocyst or results in the subsequent expulsion of a newly implanted blastocyst.
Applicants have made the important discovery that the compounds of the present invention exhibit marked antiprogestational and antifertility properties without substantial interference with other biological processes. Thus, under certain dosage regimens, as for example, a daily, low-dosage regimen, the instant compounds are able to reduce fertility in mammals as a consequence of their antiprogestational activity without interfering with normal ovulation. In this regard these compounds differ from the contraceptive steroids of the prior art which function by inhibiting ovulation, by interfering with ovum transport or by virtue of their progestational and/or estrogenic properties.
Administration of the antiprogestational agents of the present invention during the normal menstrual cycle of primates apparently causes a desynchronization of the maturing uterine mucosa relative to the process of ovulation, thereby preventing implantation or nidation of the fertilized ovum. Thus, in women, for example, the withdrawal of progesterone from a progesterone-primed endometrium results in menstrual bleeding. Periodic administration of the antiprogestational agents of the present invention, therefore, insures menstrual cyclicity in women, even when administered subsequent to ovulation.